This project seeks to relate the visual functioning of strabismic and anisometropic amblyopes to the Duplicity Theory of vision. It is anticipated that the kinds of studies necessary to accomplish this aim will: (1) contribute to a more comprehensive delineation of the physiopathology of these amblyopias; (2) provide a reassessment of the Wald-Burian pattern vision-light sensitivity dissociation hypothesis of amblyopia; and (3) determine whether the scotopic acuity of amblyopes is spared. Additionally, by selective parallel studies of non-amblyopes, it will also gather data on whether the dominant eyes of these amblyopes are normal. Since the retinal region studied frequently influences a visual function, any valid comparisons between the functions of any two eyes requires that fixation be considered. The project, therefore, has developed precise methods to measure eccentricity of fixation. The visual functions to be investigated are: (1) vernier acuity along various meridians of the visual field under photopic and scotopic conditions; (2) photopic and scotopic sensitivities and luminosities of the foveal and of the extrafoveal regions of the visual field; (3) the influence of testfield size and region tested on dark adaptation; (4) the dynamics of suppression of pattern vision by dominant eye stimulation under both photopic and scotopic conditions; and (5) the relationship between acuity and eccentricity of fixation.